1. Field of the Invention
The present invention relates to a fuel cell collector structure and a solid oxide fuel cell stack using the same. More particularly, the invention relates to the fuel cell collector structure which secures electric conduction between plate-shaped single cells and prevents a decrease in conductivity characteristics of a single cell by deformation caused by temperature change, and also relates to the solid oxide fuel cell stack using the same.
2. Description of the Related Art
Recently, the fuel cell receives attention from a viewpoint of resource saving and environmental protection. In the fuel cell, air and hydrogen are respectively used as oxidizing agent gas and fuel gas to directly convert latent chemical energy of the fuel into electric energy. Particularly, because a solid oxide fuel cell (SOFC) has many advantages such that electric power generation efficiency is high and waste heat is effectively utilized, researches and developments of SOFC are actively performed.
SOFC includes the single cell in which an air electrode made of (La, Sr)MnO3 and a fuel electrode made of NiO-yttria stabilized zirconia cermet are respectively arranged on the surfaces of a solid electrolyte layer made of yttria stabilized zirconia (YSZ), and a separator which electrically connects adjacent single cells and distributes the fuel gas and the oxidizing agent gas to the single cell.
A collector surface of the separator has conventionally been formed in a plane by machining. However, the single cell has curling or deformation generated in forming the single cell, and it is difficult to correct the deformation to the complete plane by the machining due to a material of the single cell or the like. Therefore, when the separator is attached to the single cell, the single cell does not come into contact with the whole of the collector surface of the separator, but the single cell comes into point contact with the collector surface, so that in some cases, a good electrical connection state cannot be obtained.
When a plurality of single cells are laminated, it is necessary to clamp the laminated single cells from above and below the single cell in order to stable the single cell, and clamping load is applied to the single cell through the separator. When clamping force is changed by the temperature fluctuation and the load becomes excessive, sometimes the separator or the single cell is broken.
In order to solve the above problems, there has been proposed the fuel cell collector structure in which a metal plate having a concave portion elastically comes into contact with an air electrode and a fuel electrode to release stress applied to the cell at the time of the current collection (see Japanese Patent Application Laid-Open No. 2001-68132). There has also been proposed a method of using electrically conductive felt as the collector (see Japanese Patent Application Laid-Open No. H1-012469). Further, it has been proposed that the electrically conductive felt is arranged while pressed by elastic contact (see Japanese Patent Application Laid-Open No. H6-203857).